1. Field of the Invention
This invention relates to seatbelt systems and more particularly to locking devices for seatbelt systems.
2. Prior Art
Generally, a seatbelt system is designed such that one end of a passenger-restraining seatbelt is power retracted on a retractor fixed to the vehicle such that the tension is always applied to the seatbelt. Accordingly, an intermediate portion of the seatbelt kept in close contact with a passenger so that the passenger is restrained. When the passenger releases the seatbelt, most of the seatbelt is power retracted and stored in the retractor. Furthermore, within the retractor is provided a ratchet wheel which is attached to a retractor shaft on which the seatbelt is retracted in layers. Druing a vehicular emergency, a pawl is caused to engage with the ratchet wheel so that the rotation of the ratchet wheel and the retractor shaft in the direction of the extension of the seatbelt is abruptly halted. As a result, the extension of the seatbelt during a vehicular emergency is prevented such that the passenger is securely restrained.
However, in cases where the vehicle is provided with a so-called passive seatbelt system in which the passenger is automatically caused to don the seatbelt after entering the vehicle, the seatbelt is alternately caused to approach and move away from the passenger seat when the passenger enters or leaves the vehicle so that the space between the seatbelt and the passenger seat alternately expands and contracts. As a result, the amount of seatbelt retracted on the seatbelt retractor is extremely enlarged. As a result of this large amount of seatbelt retracted on the retractor shaft, a considerable length of seatbelt continues to be extended even after the rotation of the rotation shaft in the direction of seatbelt extension has stopped during the vehicular emergency until the seatbelt is tightly wound on the retractor shaft. Thus, in spite of the fact that the rotation of the shaft in the direction of the extension of the seatbelt is stopped, restraint of the passenger is incomplete whereby the safety of the passenger is not assured by the seatbelt system.
For this reason, a locking device is required which directly locks an intermediate portion of the seatbelt between the retractor shaft and the portion of the seatbelt which restrains the passenger. However, in cases where an intermediate portion of the seatbelt is locked, it is necessary that the broad area of the seatbelt be clamped in the locking device. Otherwise, stress will be concentrated on a small clamped portion and the seatbelt will be easily broken and result in a dangerous condition for the passenger during a vehicular emergency.